RT Journal Article
SR Electronic
T1 [3H]WB4101 labels the 5-HT1A serotonin receptor subtype in rat brain. Guanine nucleotide and divalent cation sensitivity.
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 487
OP 494
VO 28
IS 6
A1 A B Norman
A1 G Battaglia
A1 I Creese
YR 1985
UL http://molpharm.aspetjournals.org/content/28/6/487.abstract
AB In the presence of a 30 nM prazosin mask, [3H]-2-(2,6-dimethoxyphenoxyethyl) aminomethyl-1,4-benzodioxane ([3H]WB4101) can selectively label 5-HT1 serotonin receptors. Serotonin exhibits high affinity (Ki = 2.5 nM) and monophasic competition for [3H] WB4101 binding in cerebral cortex. Furthermore, we have found a significant correlation (r = 0.96) between the affinities of a number of serotonergic and nonserotonergic compounds at [3H]WB4101-binding sites in the presence of 30 nM prazosin and [3H] lysergic acid diethylamide ([3H]LSD)-labeled 5-HT1 serotonin receptors in homogenates of rat cerebral cortex. Despite similar pharmacological profiles, distribution studies indicate that, in the presence of 5 mM MgSO4, the Bmax of [3H]WB4101 is significantly lower than the Bmax of [3H]LSD in various brain regions. WB4101 competition for [3H] LSD-labeled 5-HT1 receptors fits best to a computer-derived model assuming two binding sites, with the KH for WB4101 being similar to the KD of [3H]WB4101 binding derived from saturation experiments. This suggests that [3H]WB4101 labels only one of the subtypes of the 5-HT1 serotonin receptors labeled by [3H]LSD. Interestingly, the selective 5-HT1A serotonin receptor antagonist, spiperone, and the selective 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino) tetraline, exhibit high affinity and monophasic competition for [3H]WB4101 but compete for multiple [3H]LSD 5-HT1 binding sites. These data indicate that [3H]WB4101 selectively labels the 5-HT1A serotonin receptor, whereas [3H] LSD appears to label both the 5-HT1A and the 5-HT1B serotonin receptor subtypes. The divalent cations, Mn2+, Mg2+, and Ca2+ were found to markedly increase the affinity and Bmax of [3H]WB4101 binding in cerebral cortex. Conversely, the guanine nucleotides guanylylimidodiphosphate and GTP, but not the adenosine nucleotide ATP, markedly reduce the Bmax of [3H]WB4101 binding. These characteristics are typical of agonists interacting with receptors which modulate cellular function via a guanine nucleotide-regulatory subunit.